This application is a 371 of PCT/EP00/04105 filed May 8, 2000.
In chromatography a flow of liquid containing components to be removed from the liquid is allowed to pass through a separation medium. The components typically differ in their interactions with the separation medium resulting in a differential retention. The components will become at least partially separated from each other. The efficiency of a separation medium will, among others, depend on the surface area available for the solute.
There is a general desire to increase the available surface area in direct contact with the through flowing liquid. In case the liquid is aqueous and the separation media based on a hydrophobic material, a hydrophilic coating has been provided, for instance. Various thicknesses have been suggested from monomolecular and thicker layers permitting through flow in the centre of the pores (EP 221,046 and WO 9719347, respectively) up to filling the through flow pores completely (EP 288,310).
By the term xe2x80x9cthrough flowing liquidxe2x80x9d is meant that the liquid provides convective mass transport. Surfaces accessible by the through flowing liquid are therefore called xe2x80x9cconvective surfacesxe2x80x9d. Analogously pores/pore systems accessible by the through flowing liquid are called xe2x80x9cconvective pore systemsxe2x80x9d (for instance pore system 1 described below). The pore sizes of convective pore systems are typically xe2x89xa70.1 xcexcm, such as xe2x89xa70.5 xcexcm, by which is meant that a sphere xe2x89xa70.1 xcexcm respective xe2x89xa70.5 xcexcm in diameter is able to pass through. In case the media is in form of beads packed to a bed, the ratio between convective pore sizes and the diameter of the beads typically is in the interval 0.01-0.3, with preference for 0.05-0.2. Pores having sizes xe2x89xa70.1 xcexcm, such as xe2x89xa70.5 xcexcm, are often called macropores.
Separation media may also have pore systems that are only accessible by diffusion of liquid and/or of components present in the liquid (diffusive mass transport) (xe2x80x9cdiffusive pore systemxe2x80x9d, for instance pore system 2 as described below when being microporous). Diffusive pore systems are characterized in having openings into the convective pore system, which are not large enough for the liquid flow to pass through. These openings of pore system 2 are typically such that only spheres with diameters xe2x89xa60.5 xcexcm, such as xe2x89xa60.1 xcexcm, can pass through. Pores having sizes xe2x89xa60.5 xcexcm, such as xe2x89xa60.1 xcexcm, are often called micropores.
The figures for pore sizes given in the context of the present invention refer to values obtained by SEM or ESEM (scanning electron microscopy and environmental scanninmg electron microscopy, respectively) and/or by SEC (size exclusion chromatography) utilising polystyrenes and dextrans, for instance. See Hagel, xe2x80x9cPore Size Distributionxe2x80x9d in xe2x80x9cAqueous Size-Exclusion Chromatographyxe2x80x9d Elsevier Science Publisher B.V., Amsterdam, The Netherlands (1988) 119-155.
A first object is to increase the total capacity of macroporous matrices.
A second object is to increase the break through capacity of matrices comprising macropores filled up with separation media.
Total capacity and break through capacity refer to the ability of the matrices to interact with a substance present in a liquid that flows through the matrices. The interaction may relate to affinity binding between the substance and a ligand structure having affinity for the substance and being present on the support matrix. The interaction may also be a sterically restricted permeation due to the size and shape of the substance.
It has now been recognized that these objects can be met in case the macropores of a base matrix comprise an interior material that leaves a continuous free volume between the interior material and the inner walls of the macropores.
A first aspect of the invention is a support matrix comprising a) a base matrix, preferably polymeric, with macropores (pore system 1) and b) an interior material, possibly porous (pore system 2), retained within the macropores. The characterizing feature of the matrix is a continuous free volume between the interior material and the inner pore walls of the macropores. The support matrices can be in a packed or fluidised bed format or in the form of a monolithic plug. In the preferred variants the continuous free volume permits liquid flow through the matrix, preferably between two opposite ends of the matrix. The dimensions of the continuous free volume are typically selected such that at least 1%, such as at least 4%, of the liquid will pass through the matrix in the continuous free volume. For a matrix in form of a monolithic plug this means 100% liquid flow through the matrix.
The sizes of the macropores of the empty base matrix without interior material are typically in the interval 0.1-1000 xcexcm, such as 0.5-1000 xcexcm, with preference for 1-100 xcexcm (pore system 1). The base matrix may also contain a set of less pores (pore system 3) having pores in the interval 10 xc3x85-0.5 xcexcm, such as 10 xc3x85-0.1 xcexcm.
The upper limit of the pore sizes (pore system 2) depends on the pore sizes of pore system 1. In case the pores of pore system 1 are sufficiently large, pore system 2 may contain interior material that may or may not be macroporous (pore system 4). Pore system 2 is in the preferred variants microporous, i.e. its pore sizes are xe2x89xa60.5 xcexcm, such as xe2x89xa60.1 xcexcm. In case pore systems 2 and 4 are macroporous, they can be considered being a part of pore system 1.
The free volume present in the inventive matrices will increase the convective surface area. This will mean faster mass transport and increased break through capacity for interactions with solutes in a through-flowing liquid. The convective surface area of a matrix according to the invention will typically be at least 25%, such as at least 50% or at least 75%, higher than the convective surface of the base matrix without interior material.
The preferred pore systems consist of a three dimensional network of pores, which network comprises a number of pores, pore branches, pore bifurcations etc., and in the preferred variants also cavities communicating with each other via the pores. This applies to macropore systems, including convective pore systems, as well as micropore systems.
In the preferred base matrices, the macropore system is built up of cavities in the form of spheres with connecting pores between the spheres. The diameters of the spheres may be between 1 xcexcm-100 xcexcm, such as 1 xcexcm-25 xcexcm. The diameters of the connecting pores are normally about {fraction (1/10)}-⅓ of the diameters of the spheres, for instance between 0.1 xcexcm-10 xcexcm, such as 0.5 xcexcm-10 xcexcm. In case the matrices are in form of beads/particles, the cavities typically have diameters of  less than {fraction (1/9)} of the diameter of the particles.
In some preferred.variants the interior material has a size and/or form prohibiting it to leave the base matrix, i.e. is a so called xe2x80x9cjailed interior materialxe2x80x9d.
Base matrices having pore systems built up by spherical cavities with connecting pores between the cavities )are readily available from the prior art. See for instance U.S. Pat. No. 5,833,861 (PerSeptive Biosystems), EP 288,310 (Unilever), EP 68310 (Unilever), WO 9719347 (Amersham Pharmacia Biotech AB), U.S. Pat. No. 5,334,310 (Cornell Research Foundation), WO 9319115 (Amersham Pharmacia Biotech AB) etc.
The base matrices may in principle be based on materials that in the field are per se known for the manufacture of chromatographic adsorbents in form of monolithic plugs or particles. Thus the main constituent in the base matrix can god be based on organic polymers, such as native polymers (so called biopolymers) and synthetic polymers, and inorganic material. The interior material is primarily based on organic polymers that may be native or synthetic.
Illustrative examples of biopolymers are polysaccharides such as dextran, agarose, cellulose, carageenan, alginate, pullulan, and starch, including also chemically modified forms. Macroporous forms of polysaccharides are best obtained according to the method described in WO 9319115 (Amersham Pharmacia Biotech AB), i.e. initially a water solution containing the polysaccharide material is prepared which then is suspended in a an organic liquid immiscible with water to form an emulsion that upon cooling gives a macroporous block. The method can be modified to give macroporous beads. Macroporous polysaccharide matrices will normally contain both a macropore system (pore system 1) and a micropore system (pore system 3). The pore sizes of the macropore system can be controlled by varying the relative amount of organic liquid and by proper selection of emulsifier during the manufacture of the base matrix. The pore sizes of the micropore system can be controlled by varying the concentration of polysaccharide in the starting aqueous solution. The matrices can be stabilised by cross-linking, for instance by the use of reagents reacting bifunctionally with hydroxy groups. Bisepoxides, epihalo hydrins etc are typical cross-linking agents.
Synthetic polymers are best illustrated by so called vinyl polymers, i.e. polymers obtainable by polymerisation of compounds exhibiting one or more polymerisable alken groups, such as in vinyl benzenes, acrylic/methacrylic acid derivatives (acids, amides, nitrites esters etc). Creation of the base matrix in form of particles may take place o/w-emulsions or suspensions, for instance by polymerisation with the monomers being initially present in the oil phase. By utilizing bulk polymerization monolithic plug matrices can be obtained. By including an organic liquid (porogen) in which the monomers but not the polymer are dissolvable, base matrices having various type of pore structures will be achieved.
The base matrix can also be composed of other synthetic polymers, for instance condensation polymers in which the monomers are selected from compounds exhibiting two or more groups selected among amino, hydroxy, carboxy etc groups. Particularly emphasized monomers are polyamino monomers, polycarboxy monomers (including analogous reactive halides, esters and anhydrides), poly hydroxy monomers, amino-carboxy monomers, amino-hydroxy monomers and hydroxy-carboxy monomers, in which poly stands for two, three or more of the functional group referred to. Compounds containing a functional group that is reactive twice, for instance carbonic acid or formaldehyde, are included in polyfunctional compounds. The polymers contemplated are typically polycarbonates, polyamides, polyamines, polyethers etc.
Examples inorganic materials that in macroporous forms may be useful in base matrices are silica, zirconium oxide, graphite, tantalum oxide etc.
Preferred matrices lack groups that are unstable against hyrolysis, such as silan, ester, amide groups and groups present in silica as such.
The preferred type of base matrix is obtainable by polymerizing vinyl monomers of the above-mentioned type in a high internal phase emulsion (HIPE) giving a macropore structure comprising open interconnecting spherical cavities of the type described above. See for instance EP 288,310 (Unilever), EP 68,310 (Unilever), WO 9719347 (Amersham Pharmacia Biotech AB) and U.S. Pat. No. 5,200,433. This method has previously been extended to w/o/w emulsions in which the inner w/o-emulsion is in form of drops containing an HIPE. See for instance WO 9531485 which describes beaded forms of this type of matrices. By including a liquid porogen, a micropore system (pore system 3) will be formed in addition to the macropore system comprising spherical cavities. See under the heading xe2x80x9cPore Systemsxe2x80x9d.
In some variants the base matrix may consist of a number of minor particles that irreversibly stick together to form agglomerates. The interstices between the minor particles define the pore systems. These variants may be in the form of larger particles (for instance beads) or monolithic plugs.
The surfaces of the base matrix (for instance of pore system 1) mediating direct contact with a through flowing liquid may be hydrophobic or hydrophilic. By a hydrophilic surface is contemplated that the surface exhibits a plurality of polar groups that contain an oxygen or a nitrogen (hydrophilic groups). Suitable polar groups are hydroxy (alcohol and phenol), carboxy (xe2x80x94COOH/xe2x80x94COOxe2x88x92), ester, amide, ether (such as in polyoxyethylene) etc. By the term hydrophobic is meant that there are only a few or none of the above-mentioned hydrophilic groups. In the context of the present invention pronounced hydrophilic surfaces have a water contact angle  less than 30xc2x0.
A base matrix having hydrophobic surfaces may easily be hydrophilised according to per se known techniques. Analogously hydrophilic surfaces may be hydrophobised. Pronounced hydrophobic surfaces have a water contact angle  greater than 50xc2x0.
The interior material is typically a polymer material that preferably is porous (pore system 2).
The interior material is primarily located to macropores in the base matrix in which the macropores have sufficient sizes to provide a continuous free volume as defined above. A portion of the interior material may be located to larger micropores or to macropores not having the sufficient size for providing a continuous free volume.
The interior material may in principle be based on the same kind of materials as the base matrix. See above.
The pore size distribution of pore system 2 may be controlled during the formation of the material according to the same rules as utilized for chromatographic matrices.
The preferred interior material is based on polysaccharides.
The interior material is typically formed within the macropores of the base matrix. One method for this comprises the steps:
i) filling the macropores with a soluble form of the interior material,
ii) transforming the soluble form within the macropores to an insoluble form,
iii) shrinking the insoluble form and
iv) irreversibly stabilising the material in its shrunken form.
This method is best illustrated with polyhydroxy polymers, such as polysaccharides. Aqueous solutions can be prepared of most polysaccharides, either in a native form or in a properly derivatised form. The aqueous solutions of polyhydroxy polymers are often easily transformed to gels as known in the field, either by decreasing the temperature or by chemically derivatization, for instance cross-linking. Agarose, for instance, is known to dissolve in warm water but its solutions gels when the temperature is decreased. Similarly dextran is highly soluble in water but when cross-linked it will form a gel. Gel formation as described above in a macropore system will assist in retaining the polysaccharide within the pore system. It is known that this type of gels may be forced to shrink. Shrinking of a gel located in a macropore system will therefore form a continuous free volume of the type defined above. Properly substituted agarose in gel form, for instance, will shrink upon cross-linking under the appropriate conditions. The cross-linking at the same time leads to an irreversibly stabilised geometric form. See for instance WO 9738018 (page 7, end of 3rd paragraph). Similarly, a cross-linked dextran gel swelled in water will shrink in case the water is replaced with a less polar liquid, such as methanol. Upon cross-linking, for instance with bisepoxide or epihalohydrin, the shrunken form of the dextran gel will become irreversibly stabilised.
The general principle outlined in the preceding paragraph is valid for soluble forms of other polymers provided that the soluble forms can be transformed (shrunken) to an insoluble form that occupies a less volume and that the shrunken form can be stabilised irreversibly to this volume. The space between the interior material and the inner walls of the macropores shall be such that there is a continuous free volume, preferably permitting liquid flow through the matrix. In case a soluble form of the polymer can water, other liquids can be used. The soluble forms referred to also include monomers that are able to polymerise to an interior material.
A first alternative for steps (ii)-(iv) above comprises performing these steps essentially simultaneously. A second alternative for steps (ii)-(iv) comprises step (ii) followed by performing steps (iii) and (iv) essentially simultaneously. A third alternative for steps (ii)-(iv) comprises running the sequence step by step. The choice of alternative will depend on the starting soluble form and can be determined as outlined in the experimental part.
Typical methods for transforming a soluble form to an insoluble form (step (ii)) comprise decrease of temperature, chemical derivatization, for instance cross-linking, or solvent/liquid exchange. Typical methods for shrinking (step (iv)) comprise cross-linking, change of ionic strength, or exchange of liquids. For polymers containing a plurality of polar group, going from a more polar liquid to a less polar liquid often cause shrinking. For polymers having a pronounced hydrophobicity, for instance by being essentially free of polar groups, a shrinkage often requires exchanging a less polar with a more polar liquid. Typical methods for stabilisation (step (v)) comprise cross-linking.
A particular useful variant is to utilize a properly allylated polysaccharide, such as agarose, and carry out step (ii) according to the second alternative. The variant outlined above utilizing water-soluble polymers, such as dextran, is according to the third alternative.
The pore surfaces (of the micropores and/or the macropores) may exhibit a plurality of affinity ligands, i.e. structures with affinity for a counterpart. An affinity ligand is an individual member of an affinity pair. Affinity ligands are commonly used to affinity bind (affinity adsorb) the other member of the pair to the support matrix. Well-known affinity pairs are positively and negatively groups (ion exchange), antibodies and antigens/haptens, lectins and carbohydrate structures, IgG binding proteins and IgG, chelate groups and chelating compounds, complementary nucleic acids, hydrophobic groups on the ligand and on the counterpart etc. This type of groups may be introduced onto the support matrix by techniques well known in the field. Affinity groups are of particular interest when utilizing the novel support matrices of the present invention in separation methods based on affinity for a substance to be purified or removed from a liquid containing the substance. They may also be of interest for matrices that are used as support in cell culture and in solid phase synthesis and as support for catalysts, such as enzymes.
In case the support matrices as defined above are used for affinity adsorption, the support matrix exhibits a member of an affinity pair as defined above. The use comprises bringing the support matrix and a polar liquid, typically an aqueous liquid, or xe2x80x9cnonxe2x80x9d-polar liquid containing the other member of the affinity pair in contact with each other. The conditions are selected to promote affinity binding and are in principle regarded as per se known in the field. Subsequently the support matrix is separated from the liquid, and, if so desired, the affinity-adsorbed member can be released and further processed.